A posting source which returns a fixed weight for all documents. More...

#include <postingsource.h>

Inheritance diagram for Xapian::FixedWeightPostingSource:

Public Member Functions
	FixedWeightPostingSource (double wt)
	Construct a FixedWeightPostingSource.
Xapian::doccount	get_termfreq_min () const override
	A lower bound on the number of documents this object can return.
Xapian::doccount	get_termfreq_est () const override
	An estimate of the number of documents this object can return.
Xapian::doccount	get_termfreq_max () const override
	An upper bound on the number of documents this object can return.
double	get_weight () const override
	Return the weight contribution for the current document.
void	next (double min_wt) override
	Advance the current position to the next matching document.
void	skip_to (Xapian::docid min_docid, double min_wt) override
	Advance to the specified docid.
bool	check (Xapian::docid min_docid, double min_wt) override
	Check if the specified docid occurs.
bool	at_end () const override
	Return true if the current position is past the last entry in this list.
Xapian::docid	get_docid () const override
	Return the current docid.
FixedWeightPostingSource *	clone () const override
	Clone the posting source.
std::string	name () const override
	Name of the posting source class.
std::string	serialise () const override
	Serialise object parameters into a string.
FixedWeightPostingSource *	unserialise (const std::string &serialised) const override
	Create object given string serialisation returned by serialise().
void	reset (const Database &db_, Xapian::doccount shard_index) override
	Set this PostingSource to the start of the list of postings.
std::string	get_description () const override
	Return a string describing this object.
Public Member Functions inherited from Xapian::PostingSource
	PostingSource () noexcept
	Allow subclasses to be instantiated.
void	set_maxweight (double max_weight)
	Specify an upper bound on what get_weight() will return from now on.
double	get_maxweight () const noexcept
	Return the currently set upper bound on what get_weight() can return.
virtual PostingSource *	unserialise_with_registry (const std::string &serialised, const Registry &registry) const
	Create object given string serialisation returned by serialise().
virtual void	init (const Database &db)
	Older method which did the same job as reset().
PostingSource *	release ()
	Start reference counting this object.
const PostingSource *	release () const
	Start reference counting this object.

Detailed Description

A posting source which returns a fixed weight for all documents.

This returns entries for all documents in the given database, with a fixed weight (specified by a parameter to the constructor). This can be used to boost a sub-query by OP_AND-ing a FixedWeightPostingSource with that sub-query - this OP_AND will match the same documents as the sub-query does, but documents matching the subquery will get the specified extra weight contribution.

Constructor & Destructor Documentation

◆ FixedWeightPostingSource()

Xapian::FixedWeightPostingSource::FixedWeightPostingSource ( double wt )

explicit

Construct a FixedWeightPostingSource.

Parameters

wt	The fixed weight to return.

Referenced by clone(), and serialise().

Member Function Documentation

◆ at_end()

bool Xapian::FixedWeightPostingSource::at_end ( ) const

overridevirtual

Return true if the current position is past the last entry in this list.

At least one of next(), skip_to() or check() will be called before this method is first called.

Implements Xapian::PostingSource.

◆ check()

bool Xapian::FixedWeightPostingSource::check	(	Xapian::docid	did,
		double	min_wt )

overridevirtual

Check if the specified docid occurs.

The caller is required to ensure that the specified document id did actually exists in the database. If it does, it must move to that document id, and return true. If it does not, it may either:

return true, having moved to a definite position (including "at_end"), which must be the same position as skip_to() would have moved to.

or

return false, having moved to an "indeterminate" position, such that a subsequent call to next() or skip_to() will move to the next matching position after did.

Generally, this method should act like skip_to() and return true if that can be done at little extra cost.

Otherwise it should simply check if a particular docid is present, returning true if it is, and false if it isn't.

The default implementation calls skip_to() and always returns true.

Xapian will always call reset() on a PostingSource before calling this for the first time.

Note: in the case of a multi-database search, the docid specified is the docid in the single subdatabase relevant to this posting source. See the reset() method for details.

Parameters

did	The document id to check.
min_wt	The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Reimplemented from Xapian::PostingSource.

◆ clone()

FixedWeightPostingSource * Xapian::FixedWeightPostingSource::clone ( ) const

overridevirtual

Clone the posting source.

The clone should inherit the configuration of the parent, but need not inherit the state. ie, the clone does not need to be in the same iteration position as the original: the matcher will always call reset() on the clone before attempting to move the iterator, or read the information about the current position of the iterator.

This may return NULL to indicate that cloning is not supported. In this case, the PostingSource may only be used with a single-database search.

The default implementation returns NULL.

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

Reimplemented from Xapian::PostingSource.

References FixedWeightPostingSource().

◆ get_description()

std::string Xapian::FixedWeightPostingSource::get_description ( ) const

overridevirtual

Return a string describing this object.

This default implementation returns a generic answer. This default it provided to avoid forcing those deriving their own PostingSource subclass from having to implement this (they may not care what get_description() gives for their subclass).

Reimplemented from Xapian::PostingSource.

◆ get_docid()

Xapian::docid Xapian::FixedWeightPostingSource::get_docid ( ) const

overridevirtual

Return the current docid.

This method may assume that it will only be called when there is a "current document". See get_weight() for details.

Note: in the case of a multi-database search, the returned docid should be in the single subdatabase relevant to this posting source. See the reset() method for details.

Implements Xapian::PostingSource.

◆ get_termfreq_est()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_est ( ) const

overridevirtual

An estimate of the number of documents this object can return.

It must always be true that:

get_termfreq_min() <= get_termfreq_est() <= get_termfreq_max()

Xapian will always call reset() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

◆ get_termfreq_max()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_max ( ) const

overridevirtual

An upper bound on the number of documents this object can return.

Xapian will always call reset() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

◆ get_termfreq_min()

Xapian::doccount Xapian::FixedWeightPostingSource::get_termfreq_min ( ) const

overridevirtual

A lower bound on the number of documents this object can return.

Xapian will always call reset() on a PostingSource before calling this for the first time.

Implements Xapian::PostingSource.

◆ get_weight()

double Xapian::FixedWeightPostingSource::get_weight ( ) const

overridevirtual

Return the weight contribution for the current document.

This default implementation always returns 0, for convenience when implementing "weight-less" PostingSource subclasses.

This method may assume that it will only be called when there is a "current document". In detail: Xapian will always call reset() on a PostingSource before calling this for the first time. It will also only call this if the PostingSource reports that it is pointing to a valid document (ie, it will not call it before calling at least one of next(), skip_to() or check(), and will ensure that the PostingSource is not at the end by calling at_end()).

Reimplemented from Xapian::PostingSource.

◆ name()

std::string Xapian::FixedWeightPostingSource::name ( ) const

overridevirtual

Name of the posting source class.

This is used when serialising and unserialising posting sources; for example, for performing remote searches.

If the subclass is in a C++ namespace, the namespace should be included in the name, using "::" as a separator. For example, for a PostingSource subclass called "FooPostingSource" in the "Xapian" namespace the result of this call should be "Xapian::FooPostingSource".

This should only be implemented if serialise() and unserialise() are also implemented. The default implementation returns an empty string.

If this returns an empty string, Xapian will assume that serialise() and unserialise() are not implemented.

Reimplemented from Xapian::PostingSource.

◆ next()

void Xapian::FixedWeightPostingSource::next ( double min_wt )

overridevirtual

Advance the current position to the next matching document.

The PostingSource starts before the first entry in the list, so next(), skip_to() or check() must be called before any methods which need the context of the current position.

Xapian will always call reset() on a PostingSource before calling this for the first time.

Parameters

min_wt The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Implements Xapian::PostingSource.

◆ reset()

void Xapian::FixedWeightPostingSource::reset	(	const Database &	db,
		Xapian::doccount	shard_index )

overridevirtual

Set this PostingSource to the start of the list of postings.

This is called automatically by the matcher prior to each query being processed.

If a PostingSource is used for multiple searches, reset() will therefore be called multiple times, and must handle this by using the database passed in the most recent call.

Parameters

db	The database which the PostingSource should iterate through.
shard_index	The 0-based index indicating which shard in a multi-database db is. This can be useful if you have an external source of postings corresponding to each shard.

Note: in the case of a multi-database search, a separate PostingSource will be used for each database (the separate PostingSources will be obtained using clone()), and each PostingSource will be passed one of the sub-databases as the db parameter here. The db parameter will therefore always refer to a single database. All docids passed to, or returned from, the PostingSource refer to docids in that single database, rather than in the multi-database.

A default implementation is provided which calls the older init() method to allow existing subclasses to continue to work, but the default implementation of init() throws Xapian::InvalidOperationError so you must override either this method or init(). In new code, override this method in preference.

Since: Added in Xapian 2.0.0.

Reimplemented from Xapian::PostingSource.

◆ serialise()

std::string Xapian::FixedWeightPostingSource::serialise ( ) const

overridevirtual

Serialise object parameters into a string.

The serialised parameters should represent the configuration of the posting source, but need not (indeed, should not) represent the current iteration state.

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Reimplemented from Xapian::PostingSource.

References FixedWeightPostingSource().

◆ skip_to()

void Xapian::FixedWeightPostingSource::skip_to	(	Xapian::docid	did,
		double	min_wt )

overridevirtual

Advance to the specified docid.

If the specified docid isn't in the list, position ourselves on the first document after it (or at_end() if no greater docids are present).

If the current position is already the specified docid, this method will leave the position unmodified.

If the specified docid is earlier than the current position, the behaviour is unspecified. A sensible behaviour would be to leave the current position unmodified, but it is also reasonable to move to the specified docid.

The default implementation calls next() repeatedly, which works but skip_to() can often be implemented much more efficiently.

Xapian will always call reset() on a PostingSource before calling this for the first time.

Note: in the case of a multi-database search, the docid specified is the docid in the single subdatabase relevant to this posting source. See the reset() method for details.

Parameters

did	The document id to advance to.
min_wt	The minimum weight contribution that is needed (this is just a hint which subclasses may ignore).

Reimplemented from Xapian::PostingSource.

◆ unserialise()

FixedWeightPostingSource * Xapian::FixedWeightPostingSource::unserialise ( const std::string & serialised ) const

overridevirtual

Create object given string serialisation returned by serialise().

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Parameters

serialised A serialised instance of this PostingSource subclass.

Reimplemented from Xapian::PostingSource.

The documentation for this class was generated from the following file:

xapian/postingsource.h

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ FixedWeightPostingSource()

Member Function Documentation

◆ at_end()

◆ check()

◆ clone()

◆ get_description()

◆ get_docid()

◆ get_termfreq_est()

◆ get_termfreq_max()

◆ get_termfreq_min()

◆ get_weight()

◆ name()

◆ next()

◆ reset()

◆ serialise()

◆ skip_to()

◆ unserialise()